Comtech EF Data CDM-625A - Manual (Page 157)

CDM-625A Advanced Satellite Modem MN-CDM625A
Front Panel Operation Revision 3
6–31
Edit the SNR Alarm Point by using the ◄ ► arrow keys to select a digit, and then using the ▲▼
arrow keys to change that digit. The allowable range is from 00.1 to 16.0 dB. Press ENTER.
If the Rx SNR falls below this value and the fault is NOT masked, a receive traffic fault
will be generated.
6.2.1.5 CONFIG: Clocks
Clocking: TxClock RxBuffer/Clock
Clock-Ext Freq-Ref Int-Ref-Adjust ()
Use the ◄ ► arrow keys to select a parameter. Press ENTER.
6.2.1.5.1 CONFIG: Clocks  Tx Clock
Transmit Clock = Internal(SCT)
(Int(SCT),TxTerr(TT),RxLoop, ETTSTRxS) ()
Use the ▲▼ arrow keys to select from the options shown in parentheses. Press ENTER.
Note that:
Setting Function
Internal (SCT) This is the required setting when the Tx interface type is Audio. Indicates that the unit
will supply a clock to the DTE, which is derived from its internal high-stability source.
Tx-Terrestrial (TT) This is the required setting when the modem’s interface type is G.703. Indicates that
the unit expects to receive a clock from the DTE, to which the unit can phase-lock its
internal circuits. If no clock is detected the modem will substitute its internal clock and
generate an alarm.
Rx-Loop-timed Allows the modem’s internal clock to be phase locked to the Rx buffer clock source.
This output clock is Send Timing. Choosing Rx-Loop does not automatically select Rx-
Sat as the buffer clock source. This allows for increased flexibility for modem clock
selection. While you typically should select Rx-Sat, other selections are also available.
Example: You have an available high stability 10 MHz clock source, but the end
equipment only accepts a clock at the information data rate. Selecting Tx Clock = Rx-
Loop and Rx Buffer Clock = EXT-REF provides receive timing and send timing to the
end equipment that is sourced from the 10 MHz reference.
Ext-TT (ST = Rx Sat) Only valid if: RS422, V.35, HSSI or LVDS, Tx and Rx data rates are equal, no RS, and
no framing. This mode is available to permit a particular variation of Loop Timing. In
this mode, transmit timing is taken from the TT pins, but ST is active and gives out a
copy of the Rx Satellite Clock.
Appendix E. CLOCK MODES AND DROP & INSERT (D&I).